SUMMARY: Prior evidence reported by our laboratory indicates that the anterior pituitary is required for renewed luteal activity and nidation in western spotted skunks, which exhibit a 200-220 period of obligate delay of implantation. We have continued to collect data which suggests that corpora lutea of the prolonged preimplantation period are relatively refractive to increased endogenous gonadotropin secretion induced by injections of LH-RH. However, the degree of refractivity seems to change as the time of nidation approaches. We have therefore been testing the hypothesis that increased estrogen (and perhaps FSH) secretion induces increased numbers of LH on luteal cell membranes, thereby enhancing luteal function. So far the data we have collected have been negative and therefore neither really support or refute the hypothesis. BIBLIOGRAPHIC REFERENCES: Sinha, A.A. Mead. 1975. Ultrastructural changes in granulosa lutein cells and progesterone levels during preimplantation, implantation and early placentation in the western spotted skunk. Cell and Tissue Research 164, 179-192. Sinha, A. A. and R. A. Mead. 1976. MOrphological changes in the trophoblast, uterus, and corpus luteum during delayed implantation, and implantation in the western spotted skunk. Amer. J. Anat. (In press)